1. Prior Art Skin Cooling
The principal methods presently used for skin cooling before or during the laser treatment involve the use of a cold contacting window or cryogenic spray device. Cryogenic spray directly to the skin may reduce a skin temperature below 0 C but can freeze the skin and cause significant damage to it. Typical cold contacting windows of the prior art utilize ice water at 0 C can cool the surface of the skin to as low as about 4 C. But prior art ice water cooled cold contact window devices are inadequate to remove enough heat to prevent unwanted surface tissue damage in many applications.
Three prior art techniques are described in the following United States patents: C. Chess, Apparatus for treating cutaneous vascular lesions, U.S. Pat. No. 5,486,172; Anderson et al., U.S. Pat. No. 5,595,568; and C. Chess, Method for treating cutaneous vascular lesions, U.S. Pat. No. 5,282,797. All of these devices and methods provide for the cooling of the skin down to temperatures of about 4 C but not below it.
A different technique is described by J. S. Nelson et al., in the article xe2x80x9cDynamic Epidermal Cooling in Conjunction With Laser-Induced Photothermolysis of Port Wine Stain Blood Vessels, Lasers in Surgery and Medicine 1996;19:224-229. In this technique the direct cryogenic spray to the skin surface is used before the laser pulse delivery. This method is normally not satisfactory. The surface gets too cold and the subsurface layers are not sufficiently cooled so that unwanted damage occurs at the surface because the tissue gets too cold from the cryogen and/or unwanted damage occurs in the immediate subsurface layers because the tissue gets too hot from the laser beam.
2. Selective Photothermolysis
Dr. Leon Goldman and Dr. Rex Anderson developed the technique known as selective photothermolysis. This technique involves the use of a laser beam having absorption in targeted tissue much higher than in other tissue. Blood has very high absorption of laser radiation at about 530 nm and 575-590 nm. These frequencies are available from the double frequency Nd-YAG laser producing 532 nm light and by an argon laser producing 530 nm. Dye lasers at 577, 585 and 587 are also used in techniques that target blood vessels. These techniques have proven very successful in treating conditions known as port wine stains when the blood vessels are small and near the skin surface. The techniques do not work well for deeper, larger blood vessels.
What is needed is a better laser surgery cooling method to better control tissue temperature during laser treatments.
The present invention provides a laser treatment device and process with controlled cooling. The device contains a cooling element with high heat conduction properties, which is transparent to the laser beam. A surface of the cooling element is held in contact with the tissue being treated while at least one other surface of the cooling element is cooled by the evaporation of a cryogenic fluid. The cooling is coordinated with the application of the laser beam so as to control the temperatures of all affected layers of tissues. In a preferred embodiment useful for removal of wrinkles and spider veins, the cooling element is a sapphire plate. A cryogenic spray cools the top surface of the plate and the bottom surface of the plate is in contact with the skin. In preferred embodiments the wavelength of the laser beam is chosen so that absorption in targeted tissue is low enough so that substantial absorption occurs throughout the targeted tissue. In a preferred embodiment for treating large spider veins with diameters in the range of 1.5 mm, Applicants use an Er:Glass laser with a wavelength of 1.54 microns. In another embodiment a cooling rod is used. A first surface is in contact with the skin surface being treated and an opposite surface is contained in an anticondensation oil chamber that is optically connected to a laser beam delivering fiber optic cable. In this preferred embodiment the temperature of the rod is monitored with a thermocouple which provides a feedback signal to a processor which controls the cooling and the laser power to provide proper regulation of temperatures at all affected tissue layers. Preferred embodiments the device may be used for treating port wine stains especially those stains involving relatively deep larger blood vessels which as indicated in the Background section are not well treated with photothermalyses techniques using highly preferentially absorbed wavelengths of about 530 nm and 575 to 590 nm.